1. Field of the Invention
The present invention relates to a cleaning apparatus, and more particularly to a cleaning apparatus suitable for cleaning substrates that require a high degree of cleanliness, such as semiconductor wafers, glass substrates, or liquid crystal displays.
2. Description of the Prior Art
As semiconductor devices have become more highly integrated in recently years, circuit interconnections on semiconductor substrates become finer and the distance between those circuit interconnections have become smaller. When semiconductor substrates are processed, small particles such as particles of semiconductor material, dust particles, or crystalline protrusive particles often tend to be attached to the semiconductor substrates being processed. If a particle greater than the distance between interconnections exists on a semiconductor substrate, then the particle will short-circuit interconnections on the semiconductor substrate. Therefore, any undesirable particles on a semiconductor substrate have to be sufficiently smaller than the distance between interconnections on the semiconductor substrate. Such problem and requirement hold true for the processing of other substrates, including a glass substrate to be used as a mask, a liquid crystal panel, and so on. To meet the above requirement, there have been practiced various cleaning procedures for removing fine particles or submicron particles from semiconductor substrates.
For example, as cleaning processes for cleaning semiconductor substrates which have been polished to a high degree of cleanliness, one practice has been to use a brush or a sponge to scrub a surface of a semiconductor substrate. This process is called a scrubbing cleaning process. Another practice has been a cavitation jet cleaning process in which high-pressure water (high speed jet stream) is projected onto the substrate to generate bubbles by cavitation. This process requires that low-pressure water should be supplied to the outer circumference of the high-pressure water to generate bubbles by cavitation.
Although the scrubbing cleaning process is effective in removing contaminants attached to the surface of the substrate, it is not always effective in removing fine particles deposited in fine grooves of the substrate surface. Further, as the amount of fine particles attached to the cleaning member increases, the particles are often reattached to the current substrate or the subsequent substrates in subsequent cleaning operations.
The cavitation jet cleaning process, on the other hand, is effective in removing fine particles deposited in the fine grooves formed in the substrate surface. However, the cavitation jet cleaning process requires that cleaning liquid should be supplied in two layers including an inner high-pressure layer and an outer low-pressure layer surrounding the inner high-pressure layer, resulting in a complicated structure. Thus, this process requires a large amount of cleaning liquid. In addition, the contaminants firmly attached to the substrate surface are difficult to be removed therefrom.
The above problems hold true for other cleaning processes. While most cleaning processes can satisfactorily clean either the substrate surface or the fine grooves in the substrate, none of them can satisfactorily clean both of the substrate surface and the fine grooves. For this reason, cleaning of semiconductor substrates has conventionally been performed in multiple steps or processes.